Electronic device, conductive composition, metal filling apparatus, and electronic device manufacturing method

ABSTRACT

An electronic device includes a plurality of stacked substrates. Each of the substrates includes a semiconductor substrate, a columnar conductor, and a ring-shaped insulator. The columnar conductor extends along a thickness direction of the semiconductor substrate. The ring-shaped insulator includes an inorganic insulating layer mainly composed of a glass. The inorganic insulating layer fills a ring-shaped groove that is provided in the semiconductor substrate to surround the columnar conductor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device, a conductivecomposition, a metal filling apparatus, and an electronic devicemanufacturing method.

2. Description of the Related Art

In the field of electronic devices such as integrated circuits,semiconductor devices and chips thereof, there has been adopted a methodof two-dimensionally arranging semiconductor chips on a circuit boardand connecting them by wiring. In this method, however, as the mountingarea increases with the number of semiconductor chips, the wiring lengthalso increases, which makes it difficult to achieve compactification,higher performance, and low power consumption of electronic devices. Inthe present situation where the microfabrication technology has beenpursued to the utmost, achieving the compactification, higherperformance, and low power consumption through the microfabrication orminiaturization of semiconductor chips cannot be expected anymore.

Therefore, there has been developed a TSV (through-silicon-via)technology where stacked circuit boards are connected together withthrough-electrodes.

The TSV technology realizes a three-dimensional structure electronicdevice such as a three-dimensional system-in-package (3D-SiP). Thisenables incorporation of many functions into a small occupation area anddramatic shortening of important electrical pathways between devices,which results in high-speed processing.

However, the TSV technology has the following several problems.

(1) Insulation Between Through-Electrode and Silicon Substrate

As means for electrically insulating a through-electrode from a siliconsubstrate, Japanese Unexamined Patent Application Publication No.2008-251964 discloses a technology in which a ring-shaped isolationgroove passing through a silicon substrate is formed around athrough-electrode passing through the silicon substrate, silicon filmsare directly formed on bottom and side faces of the isolation groove,and an insulating film is then formed on the silicon films to fill thegap left within the isolation groove, wherein the silicon film whosesurface is in contact with an inner or outer peripheral side face of theisolation groove is thermally oxidized into a thermally-oxidized siliconfilm.

However, even if the through-electrode is electrically insulated fromthe silicon substrate, reactance may decrease with increase in straycapacitance, particularly in a GHz scale high-frequency area, accordingto the electrical insulating structure. Thus, a high-frequency signalleaks from the through-electrode to the silicon substrate, deterioratingsignal transmission characteristics. In order to improve the signaltransmission characteristics in a GHz scale high-frequency area,accordingly, it is necessary to make a further improvement such asincreasing the specific resistance as high as possible while decreasingthe relative permittivity at the insulating portion where thethrough-electrode is electrically insulated from the silicon substrate.

If the disclosure of Japanese Unexamined Patent Application PublicationNo. 2008-251964 is viewed from this point, since the structure is suchthat the through-electrode is electrically insulated from the siliconsubstrate by the thermally-oxidized silicon film, the signaltransmission characteristics cannot be improved beyond a level that isachieved by the electrical insulation of the thermally-oxidized siliconfilm. That is, the improvement of the signal transmissioncharacteristics is limited.

Moreover, since it is necessary to have the step of forming the siliconfilms directly on the bottom and side faces of the isolation groove, thestep of forming the insulating film on the silicon films to fill the gapleft within the isolation groove after formation of the silicon films,and also the step of thermally oxidizing the surface of the siliconfilm, the process inevitably becomes complicated and troublesome. Whenreplacing the conventional two-dimensional arrangement technology withthe TSV technology, what is important in terms of industrial massproduction is the cost/performance, but the above technology cannotsufficiently meet this requirement.

In the above technology, furthermore, since the film is used to fill upthe isolation groove, the groove width of the isolation groove has to beset at an extremely small value, for example, about 2 μm, so thatconsidering the typical thickness of a wafer, the aspect ratio of theisolation groove would be as much as 100 to 200. This makes difficultthe silicon film formation process for the isolation groove.

(2) Thermal Deterioration of Through-Electrode During Formation andJoining

When forming the through-electrode in a semiconductor chip or wafer, inwhich a circuit element has been already formed, using the above moltenmetal filling process or a plating process (via last), it is necessaryto avoid thermal deterioration of the circuit element due to heat formelting.

From the viewpoint of avoiding the deterioration of the circuit elementdue to heat for melting, it is desirable to use a metal material of alow melting point, which however results in deteriorating heatresistance of an electronic device.

For example, tin and indium, which are taken as an example of a metalmaterial for forming the through-electrode in Japanese Unexamined PatentApplication Publication No. 2002-158191, have an advantage thatdeterioration of the semiconductor circuit element due to heat formelting at the time of formation of the through-electrode can be avoidedbecause of the low melting point, but the low melting point impairsthermal reliability.

In order to realize a three-dimensional structure electronic deviceusing the TSV technology, moreover, two or more wafers or chips formedwith the through-electrodes have to be sequentially joined together withthe through-electrodes brought into alignment. As a junction material, ametal junction material may be chosen from the viewpoint of improvingelectrical characteristics and joining ability for thethrough-electrodes. The circuit board can be joined together by meltingand then solidifying the metal junction material.

Also in this case, there is a problem that the previously formed circuitelement may be thermally damaged during the melting and joining processof the metal junction material.

The same problem also occurs when forming wiring planar conductorpatterns on the surface of the wafer along with or independently of thethrough-electrodes.

(3) Occurrence of Cracks or the Like at Through-Electrode and itsSurrounding Area

As a common problem among molten metal filling processes, there has beenobserved a phenomenon that the through-electrode is cracked, theinsulating film disposed between the inner wall surface of thethrough-hole and the peripheral surface of the through-electrode ispartially broken by the through-electrode, or eventually the siliconsubstrate is cracked around the through-electrode.

This problem is not limited to the formation of the through-electrode.Also when stacking a number of circuit boards in order to realize theabove three-dimensional arrangement, the same problem may occur atterminals for connection between the circuit boards.

(4) Poor Connection Between Through-Electrode and Conductor Pattern

From a functional perspective, the through-electrode has to beconnected, at least at one end, to a conductor pattern formed on thesubstrate. However, if the surface of the conductor pattern is oxidized,poor connection may occur between the through-electrode and theconductor pattern.

As general means for solving this problem, the reduction effect of aflux may be used for reducing the oxide film of the conductor pattern.

However, putting the flux into a minute space along with the moltenmetal material generates a flux gas. In electronic devices of this type,the minute space is a minute hole having a hole diameter of, forexample, tens of μm or less and also a considerably high aspect ratio.If the flux gas is generated within the thus-shaped minute space, ofcourse, the gas cannot easily escape, creating voids due to the flux gasaround the through-electrode, which results in reduction of sectionalarea of the columnar conductor, increase of electrical resistance, andeventually poor connection to the conductor pattern and increase ofjunction resistance.

This problem is not limited to the formation of the vertical electrode.Also when stacking a number of circuit boards in order to realize thethree-dimensional arrangement, it may result in poor connection atterminals for connection between the circuit boards, increase ofelectrical resistance, and increase of junction resistance.

(5) Difficulty of Molten Metal Filling into Minute Space

When forming the through-electrode, it is extremely difficult tosufficiently fill a high-aspect ratio minute space with a fillingmaterial down to the bottom thereof without causing voids or deformationafter hardening.

Wafers to be used for manufacturing a semiconductor device are providedwith a large number of minute spaces (holes) for formation of electrodesor the like, and the minute spaces are extremely small, for example,with a hole diameter of tens of it μm or less. In addition, thethickness of the wafer is considerably large as compared with the minutespace having such a small hole diameter, so that the minute space quiteoften has an aspect ratio of 5 or more. In order to form thethrough-electrode, a conductive material has to be reliably filled intosuch a small, high-aspect ratio minute space down to the bottom thereof,which of course requires an advanced filling technology.

As the electrode formation technology, although the technology of usinga conductive past that is a mixture of a conductive metal component andan organic binder has been known, attention is now being given to ametallurgical technology using a molten metal material that has superiorelectrical conductivity, low loss, and excellent high-frequencycharacteristics. For example, such a technology is disclosed in JapaneseUnexamined Patent Application Publication No. 2002-237468 (hereinbelowreferred to as Document 1), Japanese Unexamined Patent ApplicationPublication No. 2006-203170 (hereinbelow referred to as Document 2), andJapanese Unexamined Patent Application Publication No. 2002-368082(hereinbelow referred to as Document 3).

In Documents 1 and 2, at first, disclosed is a technology of filling ametal into a minute space (through-hole) by means of a metal fillingapparatus adopting a molten metal refilling process. The molten metalrefilling process refers to a process of reducing the pressure of anatmosphere in which a target (wafer) is placed, then inserting thetarget into a molten metal while keeping the reduced pressure, thenincreasing the atmospheric gas pressure around the molten metal so thatthe molten metal can be filled into the space with the difference inatmospheric gas pressure between before and after the insertion into themetal, and then pulling the target out of the molten metal bath forcooling in the air.

In the metal filling apparatus, two rooms, each of which is providedwith a pressure increasing/reducing means, are vertically arrangedwithin a chamber and separated from each other by a switching valve.Then, the wafer being a target is held in a suspended state by a carrierjig, dipped into a molten metal bath placed in the lower room, and thenmoved to and cooled in the upper room for hardening the molten metalwithin the minute space.

With the metal filling apparatus, however, when the target is pulled outof the molten metal bath, the molten metal within the minute space maybe drawn out by the molten metal in the bath or allowed to drip from orbead within the space under the influence of surface tension of themolten metal and the like.

Accordingly, when the target is pulled out of the molten metal bath andthen cooled, the surface of the metal within the minute space may berecessed to a level lower than the surface of the target. This may causedefective electrical continuity to the outside.

In order to avoid this, the molten metal has to be supplied again forfilling the recess. In order to fill the recess, moreover, the surfaceof the supplied metal has to be set higher than the surface of thetarget, which requires a process of matching the surface of the metalwith the surface of the target, for example, a CMP (chemical mechanicalpolishing) process. This may result in complicating the process andcausing an ensuing decrease in yield.

A further serious problem is that although the complicated process isrequired as described above, voids due to insufficient filling of themolten metal may be created in the minute space, particularly at thebottom thereof.

Furthermore, because of its complicated structure, this apparatus isdifficult to maintain and unfavorable in view of cost.

On the other hand, Document 3 discloses a metal filling apparatusadopting a differential pressure filling process. In the differentialpressure filling process, after a target (sample) formed with a minutespace and a metal sheet attached to the target are placed in a vacuumchamber, the pressure of the vacuum chamber is reduced, the metal sheetis melted by heating means, and then the pressure of the vacuum chamberis increased to a level higher than the atmospheric pressure by aninactive gas. With this, the molten metal can be vacuum sucked into theminute space. Subsequently, the vacuum chamber is opened, the moltenmetal left on the sample surface is removed, and then it is cooled inthe air at room temperature.

Document 3 claims that it has an advantage that the sample will never bewarped or cracked because its molten metal has a lower heat capacity ascompared with the molten metal refilling process (Document 1) and thatcost reduction can be achieved because the excess metal can beminimized.

With the differential pressure filling process described in Document 3,however, the molten metal cannot be completely filled into the minutespace down to the bottom thereof, which creates voids within.

In addition, since the molten metal left on the sample surface has to beremoved, a part (upper end) of the molten metal filled into the minutespace may also be scraped off during the process. Accordingly, theproblem of the recessed surface remains unsolved.

Moreover, this apparatus is also unfavorable in view of cost andprocessing efficiency because it takes long time to prepare a metalsheet previously shaped in conformity with the shape of the target andto attach the metal sheet onto the target through a solder ball or thelike.

In fact, any wafers manufactured by the differential pressure fillingprocess and devices using the same have not yet been supplied to themarket, which proves that the above problem remains unsolved.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electronicdevice, a conductive composition, a metal filling apparatus, and anelectronic device manufacturing method, which are capable of solving atleast one of the several problems concerning the TSV technology.

1. Electronic Device

An electronic device according to the present invention is formed bystacking a plurality of substrates. Each of the substrates includes asemiconductor substrate, a columnar conductor(or vertical conductor),and a ring-shaped insulator. The columnar conductor extends along athickness direction of the semiconductor substrate. The ring-shapedinsulator includes an inorganic insulating layer, and the inorganicinsulating layer fills a ring-shaped groove that is provided in thesemiconductor substrate to surround the columnar conductor.

In each of the stacked substrates of the electronic device according tothe present invention, as described above, since the ring-shapedinsulator is formed within the ring-shaped groove that is provided inthe semiconductor substrate to surround the columnar conductor, thecolumnar conductor, for example, such as a through-electrode can beelectrically insulated by the ring-shaped insulator from other adjacentcolumnar conductors.

In addition, the ring-shaped insulator contains an inorganic insulatinglayer. The inorganic insulating layer is mainly composed of a glass andfills the ring-shaped groove. For the glass component, a material havinga low relative permittivity and a high specific resistance may beselected for use among various glass materials. Therefore, the relativepermittivity and specific resistance of the ring-shaped insulator as awhole can be adjusted by the selection of the glass material, therebyreducing signal leakage in a high-frequency area and improving signaltransmission characteristics. Moreover, a dense insulating structure canbe realized without any voids because of its filled structure.

Furthermore, since the inorganic insulating layer is a filled layer,there is no reason to decrease the groove width of the ring-shapedgroove unlike the prior art which requires a deposition process. Thissimplifies the formation process of the inorganic insulating layer and,eventually, the formation process of the ring-shaped insulator.

The inorganic insulating layer can be formed by filling a liquid glass,i.e., a glass paste into the ring-shaped groove and then hardening it.Thus, a low-cost electronic device substrate can be realized using sucha simple and inexpensive process of filling a liquid glass into aring-shaped groove.

In addition to the glass component, the inorganic insulating layer maycontain a ceramic component being a sintered compact or particle. Therelative permittivity and specific resistance of the ring-shapedinsulator as a whole can also be adjusted by selecting the relativepermittivity and specific resistance for the ceramic component to becontained. This reduces signal leakage in a high-frequency area andimproves signal transmission characteristics.

The ring-shaped insulator may have insulating layers on inner wallsurfaces of the ring-shaped groove. This insulating layer preferablyincludes an oxide layer, more preferably a nitride layer. The oxidelayer and the nitride layer may be a single layer or multiple layers. Inaddition, the oxide layer and the nitride layer may be a layer depositedon an inner surface of the ring-shaped groove or a layer obtained byoxidizing or nitriding the surface of the semiconductor substrate whichappears on the inner surfaces of the ring-shaped groove. This insulatingstructure makes it possible to avoid a negative effect of thering-shaped insulator, particularly a negative effect of the glasscomponent contained in the inorganic insulating layer, on thesemiconductor substrate.

In the electronic device according to the present invention, asdescribed above, between adjacent ones of the plurality of stackedsubstrates, connection conductors are joined to each other through ajunction film. The junction film preferably contains a first metal oralloy component and a second metal or alloy component having a highermelting point than the first metal or alloy component, whereby a meltingtemperature is made higher than the melting point of the first metal oralloy component.

Since the junction film for joining the connection conductor of one ofadjacent substrates to the connection conductor of the other substratecontains the first metal or alloy component and the second metal oralloy component, as described above, the small size effect occurs at thetime of joining because of the small film thickness of the junctionfilm, allowing the second metal or alloy component to melt at atemperature close to the melting point of the first metal or alloycomponent. At this time, since the first metal or a low melting pointmetal of the alloy component is consumed by reacting with the connectionconductor and forming an intermetallic compound, the melting pointincreases considerably after joining.

In addition, since the first metal or alloy component reacts with thesecond metal or alloy component, the melting temperature of the junctionfilm after solidification increases to a temperature close to themelting point of the second metal or alloy component, i.e., atemperature that is higher the melting point of the first metal or alloycomponent at the very least.

According to the present invention, therefore, it is possible to realizea highly heat-resisting electronic device which requires a low heattreatment temperature during the joining process but can secure a highmelting point after solidification.

2. Conductive Composition

In order to realize the electronic device according to the presentinvention, it is desirable that the columnar conductor and the junctionfilm can be melted at a low temperature but have a higher melting pointafter melt-solidification. A conductive composition according to thepresent invention satisfies such characteristics and includes firstmetal particles and second metal particles. The first metal particleshave an average particle size in such a nm range as to exhibit smallsize effect, enabling melting at a temperature lower than a meltingpoint, and melting of the first metal particles causes melting of thesecond metal particles.

It is known that most metal particles can be melted at a temperaturelower than the melting point by reducing their particle size. This isbecause the occupancy of surface atoms increases with reduction of theparticle size. In this specification, the melting point reduction effectdue to the refining is referred to as “small size effect”.

In the present invention, since the first metal particles have anaverage particle size in such a nm range as to exhibit small sizeeffect, the melting point reduction effect can be obtained because ofthe small size effect.

If the particle size (diameter) of the metal particle is reduced to alevel as small as a de Broglie wavelength of atoms (several nm to 20nm), electrons are confined within that area, which leads to discreteelectronic density of states. Moreover, since freedom of movement ofelectrons is extremely limited, their kinetic energy increases. Thisphenomenon is called “quantum size effect” which is the ultimate levelof the melting point reduction due to the small size effect, wherein thefirst metal particles can be melted at a temperature of, for example,250° C. or less, preferably, 200° C. or less, more preferably, 180° C.or less.

The conductive composition according to the present invention includesnot only the first metal particles but also the second metal particles.Melting of the second metal particles is caused by melting of the firstmetal particles. Specifically, the second metal particles may be made ofa material having a melting point lower than a melting temperature ofthe first metal particles.

Therefore, columnar conductors and wiring conductor patterns can beformed without causing thermal deterioration of a previously formedsemiconductor circuit element even if the columnar conductors and wiringconductor patterns are formed on a chip or wafer by melt-solidifying theconductive composition according to the present invention. In addition,heat resistance due to a high melting point of the first metal particlescan be secured after solidification.

The conductive composition according to the present invention may beused for various electronic devices as a columnar conductor filling avertical hole bored into a substrate along a thickness direction or anelectrode material for forming wiring patterns on a substrate surface.When filling a vertical hole bored into a substrate along a thicknessdirection, it serves not only as the columnar conductor but also as afilling material.

When forming a three-dimensional system-in-package (3D-SiP), moreover,it can be used as a junction material for joining together stackedsubstrates. In any case, since its melting temperature is low but a highmelting point can be secured after solidification, it is possible torealize a highly reliable electronic device.

3. Structure of Columnar Conductor

In the electronic device according to the present invention, thecolumnar conductor included in the substrate is closely related toperformance and reliability of the electronic device. Therefore, it isintended to provide a high-performance and highly reliable columnarconductor. The columnar conductor is a metal or alloy melt-solidifiedproduct disposed in the substrate, has an equiaxed crystal area at leastin an area opposed to the substrate, and contains bismuth (Bi) andgallium (Ga) as an inoculant within the melt-solidified product.

In the present invention, as described above, since the columnarconductor is a metal or alloy melt-solidified product and has anequiaxed crystal area at least in an area opposed to the substrate,there is obtained an isotropy due to the equiaxed crystal structure.This suppresses the occurrence of cracking of the columnar conductor,breaking of the insulating film, and cracking of the substrate.

In addition, since the bismuth (Bi) and gallium (Ga) contained in themelt-solidified product as an inoculant have a negative volume change,they can suppress columnar crystal growth effectively and are thereforesuitable for nucleation of the above equiaxed crystal area.

At least in an area opposed to the substrate, moreover, the equiaxedcrystal area preferably accounts for a larger area of the columnarconductor than the columnar crystal area. With this relationship, theisotropy of the equiaxed crystal becomes more predominant at least inthe area opposed to the substrate, which suppresses more effectively theoccurrence of cracking of the electrode, breaking of the insulatingfilm, and cracking of the substrate.

One embodiment of the columnar conductor is a planar wiring which can berealized by forming, on one surface of the substrate, minute spaceswithin a mask frame or the like, filling a molten metal into the minutespaces, which serve as a mold, and then solidifying it.

If the columnar conductor is a through-conductor or anon-through-conductor, the substrate has a through-hole ornon-through-hole, and the columnar conductor is joined to an innersurface of the hole with the equiaxed crystal area disposed at least inan area that is in contact with the inner surface of the hole. Thiscolumnar conductor can be realized by filling a molten metal into thehole of the substrate, which serves as a mold, and then solidifying it.

Another proposal concerning the columnar conductor is for the case wherethe substrate includes a first conductor, a columnar conductor, and ajunction film. The first conductor is disposed on one side of thesubstrate and opposed to a bottom of a through-hole of the substrate.The columnar conductor contains a Sn alloy and fills the through-hole ofthe substrate with its bottom face opposed to the first conductor at thebottom of the through-hole.

The junction film is a metal other than noble metals and has a highermelting point than the Sn alloy. Moreover, the junction film is disposedbetween the bottom face of the columnar conductor and the firstconductor inside the bottom of the through-hole and diffused into thecolumnar conductor to produce an alloy area, thereby joining the firstconductor to the columnar conductor.

The above junction structure can be produced by a simple process ofsupplying a molten metal for forming the columnar conductor to a metalfor forming the junction film and then cooling it. As compared with thecase of a plating technology, therefore, the number of processing stepsand the processing time can be decreased and shortened considerably.Accordingly, there can be realized a low-cost three-dimensionalarrangement electronic device.

Moreover, the process of how the high melting point metal for formingthe junction film is melted and diffused into the molten metalcontaining the Sn alloy to produce an alloy area can be described inaccordance with a known phase diagram. According to the phase diagram,even if metal particles have a higher melting point than the Sn alloy,they can be melted at a temperature of 250° C. or less. Therefore,joining of the columnar conductor to the first conductor can be realizedat a low temperature, avoiding thermal damage to a semiconductor circuitelement which may be contained in a circuit board.

Furthermore, since the alloy area, which is produced by diffusion of thehigh melting point metal for forming the junction film into the columnarconductor containing the Sn alloy, has a higher melting point than atthe time of thermal diffusion, there can be obtained a conductor joiningstructure excellent in thermal stability.

Since the high melting point metal for forming the junction film isreduced in the melting process, a reduction process with a flux is notnecessary. Accordingly, the occurrence of voids due to the flux can besuppressed, which makes it possible to realize an electronic devicewhich avoids reduction of sectional area of the columnar conductor,increase of electrical resistance, and eventually poor connection to thefirst conductor and increase of junction resistance.

4. Metal Filling Apparatus

In order realize the electronic device according to the presentinvention, the columnar conductor has to be formed. A metal fillingapparatus according to the present invention is suitable for formationof such a columnar conductor. This metal filling apparatus is anapparatus for filling a molten metal into a minute space of a substrate(wafer) and includes a support, a molten metal supply unit, and apressurizing means.

The support includes a processing chamber for processing the wafer, afirst member with a mounting surface for mounting of the wafer, and asecond member with a metal supply path leading to the processingchamber. The processing chamber is defined by combining the first memberand the second member.

The molten metal supply unit is designed to fill the minute space of thewafer, which is mounted on the mounting surface, with the molten metalthrough the metal supply path. Then, the pressurizing means is designedto apply a pressure to the wafer and the molten metal filled into theminute space.

In the metal filling apparatus according to the present invention, asdescribed above, since the processing chamber of the support has themounting surface for mounting of the wafer and the molten metal supplyunit is designed to fill the minute space of the wafer, which is mountedon the mounting surface, with the molten metal through the metal supplypath, a process of pulling the wafer out of a molten metal bath is notnecessary. Thus, there is no possibility of causing a problem that themolten metal within the minute space may be drawn out by the moltenmetal in the bath or allowed to drip from or bead within the space underthe influence of surface tension of the molten metal and the like.Accordingly, the minute space can be filled with the metal materialwithout creating any cavities or voids.

In addition, since the metal filling apparatus according to the presentinvention includes the pressurizing means and the pressurizing means isdesigned to apply a pressure to the wafer and the molten metal filledinto the minute space, the molten metal can be sufficiently filled intothe minute space down to the bottom thereof and deformation of the metaldue to thermal contraction can be suppressed. Accordingly, the minutespace can be filled with the metal without creating any cavities orvoids.

In the case where the minute space is a through-hole, moreover, sincethe support supports the wafer from the side opposite from an opening ofthe minute space, which is exposed to the processing chamber, the otheropening can be closed on the surface supporting the wafer. Therefore,the molten metal within the minute space can be sufficiently pushed intothe minute space with the pressure being applied in one direction fromthe exposed opening, while the molten metal is prevented from leakingfrom the other closed opening.

Also in the case where the minute space is a non-through-hole, needlessto say, the pressure can be similarly applied in one direction from theopening without causing leakage of the molten metal.

Accordingly, the metal filling apparatus according to the presentinvention can also prevents the molten metal from having a recessedsurface which would otherwise be caused by cooling in the minute gap.This reliably secures electrical continuity to the outside.

Since the metal is prevented from having a recessed surface, moreover,resupply of a molten metal or a CMP process is not necessary aftercooling, which contributes to simplification of the process and improvedyield.

The above pressurizing means may be provided using at least one selectedfrom a gas pressure, a pressing pressure, an injection pressure, arolling pressure, a centrifugal force, and a magnetic force. Whenutilizing the gas pressure among them, a pressure control unit may beprovided for controlling a pressure within the processing chamber, andthis pressure control unit can double as the pressurizing means.

When utilizing the injection pressure, on the other hand, thepressurizing means and the molten metal supply unit may be provided byan injection machine. The injection machine may be adapted not only tosupply the molten metal to the processing chamber by injection but alsoto continue giving its injection pressure to the processing chamberuntil the molten metal filled into the minute space is hardened bycooling. When utilizing the pressing pressure, on the other hand, apress may be employed as the pressurizing means.

At an early stage of the hardening step in the pressurizing operation,preferably, not only static pressure but also dynamic pressure isactively utilized to perform dynamic pushing by the dynamic pressure.With this method, creation of unfilled areas at the bottom can beavoided more reliably by making the molten metal certainly reach thebottom of the minute space.

More preferably, the molten metal supply unit supplies the molten metalsuch that a metal film is formed over the opening. With this, the moltenmetal can be certainly pushed into the minute space with a compellingexternal force received by the metal film.

In the case where the molten metal supply unit supplies the molten metalsuch that a metal film is formed over the opening, as described above,the metal filling apparatus is preferably provided with a means forremelting the metal film over the opening after hardening of the moltenmetal and wiping off the remelted metal film. Although heat forremelting is also conducted to the hardened metal within the minutespace, since the hardened metal has a considerably higher heat capacitythan the metal film, remelting of the metal film will never lead toremelting of the hardened metal. Thus, a flat surface without any recesscan be formed by wiping off only the metal film. Alternatively, themetal film left over the opening may be mechanically removed withoutremelting.

It should be noted that in this specification, the term “metal” maysometimes be used as an idea including an alloy containing two or moremetal elements, in addition to a metal of a single element.

The other objects, constructions and advantages of the present inventionwill be further detailed below with reference to the attached drawings.However, the attached drawings show only illustrative examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a portion of an electronic deviceaccording to the present invention;

FIG. 2 is a sectional view taken along line II-II of FIG. 1;

FIG. 3 is an enlarged sectional view showing a portion of the electronicdevice of FIGS. 1 and 2;

FIG. 4 is a plan view showing a portion of another embodiment of anelectronic device according to the present invention;

FIG. 5 is a sectional view showing an embodiment of a substrateconnecting structure in the electronic device of FIGS. 1 to 4;

FIG. 6 is a sectional view of an interposer to be used for an electronicdevice according to the present invention;

FIG. 7 is a schematic enlarged view showing a conductive compositionaccording to the present invention;

FIG. 8 is a schematic sectional view showing one embodiment of asubstrate to be used for an electronic device according to the presentinvention;

FIG. 9 is a schematic enlarged view showing an equiaxed crystalstructure of the electronic device substrate of FIG. 8;

FIG. 10 is a view showing a production process of the substrate of FIGS.8 and 9;

FIG. 11 is a view showing a step after the step of FIG. 10;

FIG. 12 is a schematic sectional view showing a substrate in which acolumnar crystal structure is predominant;

FIG. 13 is a schematic view showing a problem of the substrate of FIG.12;

FIG. 14 is a SEM photograph of a substrate to be used for an electronicdevice according to the present invention;

FIG. 15 is a SEM photograph of a substrate being a comparative example;

FIG. 16 is a schematic sectional view showing another embodiment of asubstrate to be used for an electronic device according to the presentinvention;

FIG. 17 is a view showing still another embodiment of a substrate to beused for an electronic device according to the present invention;

FIG. 18 is a view showing a production process of the electronic devicesubstrate of FIG. 17;

FIG. 19 is a view showing a step after the step of FIG. 18;

FIG. 20 is a SEM photograph of a conventional substrate being acomparative example;

FIG. 21 shows the SEM photograph of FIG. 20 on an enlarged scale;

FIG. 22 is a SEM photograph of a substrate to be used for an electronicdevice according to the present invention;

FIG. 23 shows the SEM photograph of FIG. 22 on an enlarged scale;

FIG. 24 shows the SEM photograph of FIG. 22 on a further enlarged scale;

FIG. 25 is a view showing another embodiment of a substrate to be usedfor an electronic device according to the present invention;

FIG. 26 is a view showing a production process of the electronic devicesubstrate of FIG. 25;

FIG. 27 is a view showing a step after the step of FIG. 26;

FIG. 28 is a view showing another production process of the electronicdevice substrate of FIG. 25;

FIG. 29 is a view showing a step after the step of FIG. 28;

FIG. 30 is a view showing a configuration of a metal filling apparatus(before filling) according to the present invention;

FIG. 31 is a view showing a configuration of a metal filling apparatus(after filling) according to the present invention;

FIG. 32 is an enlarged sectional view of a metal filling apparatusshowing a process of filling a metal into a minute space;

FIG. 33 is an enlarged sectional view of a metal filling apparatusshowing a process of filling a metal into a minute space;

FIG. 34 is an enlarged sectional view of a metal filling apparatusshowing a process of filling a metal into a minute space;

FIG. 35 is an enlarged sectional view of a metal filling apparatusshowing a process of filling a metal into a minute space;

FIG. 36 is an enlarged sectional view of a metal filling apparatusshowing a process of filling a metal into a minute space;

FIG. 37 is a sectional SEM photograph of a semiconductor wafer (siliconwafer) obtained by a metal filling apparatus according to the presentinvention, wherein pressurized cooling was omitted;

FIG. 38 is a sectional SEM photograph of a semiconductor wafer (siliconwafer) obtained by a metal filling apparatus according to the presentinvention, wherein pressurized cooling was performed;

FIG. 39 is a view showing another embodiment of a metal fillingapparatus (before filling) according to the present invention;

FIG. 40 is a view showing another embodiment of a metal fillingapparatus (after filling) according to the present invention;

FIG. 41 is a view showing an embodiment in which a metal fillingapparatus is provided with an external force generating means (beforegenerating an external force); and

FIG. 42 is a view showing an embodiment in which a metal fillingapparatus is provided with an external force generating means (aftergenerating an external force).

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. Electronic Device

As shown in FIGS. 1 and 2, typically, an electronic device according tothe present invention is constructed in the form of a three-dimensionalsystem-in-package (3D-SiP). Specifically, it may be a system LSI, amemory LSI, an image sensor, a MEMS, or the like. Examples of theelectronic device also include an analog or digital circuit, a memorycircuit such as DRAM, and a logic circuit such as CPU, or the electronicdevice may be formed such that different types of circuits, e.g., ananalog high-frequency circuit and a low-frequency, low-power consumptioncircuit, are manufactured in different processes and then stackedtogether.

In the embodiment shown in FIGS. 1 and 2, the structure is such thatsubstrates SM1 to SMn being semiconductor wafers or semiconductordevices are sequentially stacked and joined together on a substrate INTbeing an interposer. Referring to FIG. 3, each of the substrates SM1 toSMn includes a semiconductor substrate 1A, a columnar conductor 2A, anda ring-shaped insulator 3A. The semiconductor substrate 1A is, forexample, a silicon substrate. The thickness of the semiconductorsubstrate 1A may be, but not limited to, about 50 to 700 (μm).

The columnar conductor 2A extends along the thickness direction of thesemiconductor substrate 1A. The columnar conductors 2A are distributedin rows on a substrate surface. In this embodiment, the columnarconductor 2A is a through-conductor penetrating the semiconductorsubstrate 1A.

In an X-Y plane assumed on the substrate surface, as shown in FIG. 1,the columnar conductors 2A are arranged in rows, for example, in theform of matrix, at a given arrangement pitch Dx, Dy in X, Y directions.The arrangement pitch Dx, Dy of the columnar conductors 2A is, forexample, in the range of 4 to 100 (μm), wherein a maximum diameter D1is, for example, in the range of 0.5 to 25 (μm). However, thearrangement pitch Dx, Dy is not required to be constant, and thediameter D1 is not limited to the above value, either.

The columnar conductors 2A may be formed by applying a known technologysuch as a plating process, the above-described molten metal fillingprocess, or a conductive paste filling process. Materials for formingthe columnar conductor 2A may be different for different formationprocesses.

In the case of the plating process, a Cu plating film is widely used. Inthe case of the molten metal filling process, use can be made of afilling material containing at least one selected from the groupconsisting of Sn, In, Bi, Sb and Ga and at least one selected from thegroup consisting of Cr, Cu, Ag, Au, Pt, Pd, Ni, a Ni—P alloy and a Ni—Balloy.

Regardless of which formation process is adopted, a vertical hole(through hole via) 20A has to be formed previously. The vertical hole(through hole via) 20A may be formed by a known technology such as a CVDprocess or a laser drilling process.

The ring-shaped insulator 3A is disposed within a ring-shaped groove 30Athat is provided in the semiconductor substrate 1A to surround thecolumnar conductor 2A. In the semiconductor substrate 1A, accordingly,the ring-shaped insulator 3A separates an inner ring-shaped portion 11Afrom an outer portion. Thus, the columnar conductor 2A can beelectrically insulated from other adjacent columnar conductors 2A by thering-shaped insulator 3A.

The ring-shaped groove 30A may be formed by the means used for formationof the vertical hole 20A. The ring-shaped groove 30A penetrates thesemiconductor substrate 1A along the thickness direction and has a firstinside diameter D2 larger than the diameter D1 of the vertical hole 20Ain which the columnar conductor 20A is disposed. Between the innerperipheral surface of the vertical hole 20A and the inner peripheralsurface of the ring-shaped groove 30A with the first inside diameter D2,accordingly, the semiconductor substrate 1A is left like an island by adiameter difference (D2−D1), providing the ring-shaped portion 11A.

The ring-shaped groove 30A also has a second inside diameter D3separated from the first inside diameter D2 by a groove width. That is,the ring-shaped groove 30A has a groove width (D3−D2). The groove width(D3−D2) is set at a value which will not interfere with formation of thering-shaped insulator. Its aspect ratio is 200 or less, preferably 100or less.

The ring-shaped insulator 3A includes an inorganic insulating layer 33A.The inorganic insulating layer 33A is mainly composed of a glass andcompletely fills up the ring-shaped groove 30A. Thus, a dense insulatingstructure can be realized without any voids.

The ring-shaped insulator 3A may be a single layer or may have acoaxially, spacedly arranged multilayer structure. In addition, itsshape is not limited to the illustrated circular shape but may be apolygonal shape such as a rectangular shape shown in FIG. 4. Moreover,the columnar conductor 2A is not limited to the illustrated circular orcylindrical shape, either, but may have a prismatic shape.

The inorganic insulating layer 33A may be formed by filling a liquidglass, i.e., a glass paste into the ring-shaped groove 30A and thenhardening it under pressure. Thus, the inorganic insulating layer 33Acan be formed by a simple and inexpensive process of filling a liquidglass into the ring-shaped groove 30A and hardening it.

Furthermore, since the inorganic insulating layer 33A has a filledstructure, there is no reason to decrease the groove width of thering-shaped groove 30A unlike the prior art which requires a depositionprocess. This simplifies the formation process of the inorganicinsulating layer 33A and, eventually, the formation process of thering-shaped insulator 3A.

As an example of the glass filling process, there may be taken a processof pouring a liquid glass into the ring-shaped groove 30A underreduced-pressure atmosphere and then hardening the liquid glass withinthe ring-shaped groove 30A while pressurizing with a pressing pressure,a gas pressure or a rolling pressure applied thereto.

Various materials may be used as a glass material. For example, use canbe made of a glass material containing at least one of SiO₂, PbO, B₂O₃,ZnO, MgO, Al₂O₃, Na₂CO₃, CaCO₃, Na₂O, CaO and K₂O. Among these glassmaterials, a material having a low relative permittivity and a highspecific resistance may be selected for use. This enables adjustment ofthe relative permittivity and specific resistance of the ring-shapedinsulator 3A as a whole, thereby reducing signal leakage in ahigh-frequency area and improving signal transmission characteristics.

In addition to the glass component, the inorganic insulating layer 33Amay contain a ceramic component being a sintered compact, particularly,nm-sized ceramic particles. In this case, it is possible to select therelative permittivity and specific resistance for the ceramic componentto be contained, which also enables adjustment of the relativepermittivity and specific resistance of the ring-shaped insulator 3A asa whole, reducing signal leakage in a GHz scale high-frequency area andimproving signal transmission characteristics.

Examples of the ceramic material include alumina (Ai₂O₃), mullite(3Al₂O₃·2SiO₂), cordierite (2MgO·2Al₂O₃·5SiO₂), steatite (MgO·SiO₂),forsterite (2MgO·SiO₂), silicon nitride (Si₃N₄), and aluminum nitride(AlN), whose specific resistance at a normal temperature exceeds10¹⁴(Ω·cm) and relative permittivity is in the range of 4 to 9.

The ring-shaped insulator 3A may further include insulating layers 31A,32A. The insulating layers 31A, 32A preferably include an oxide layer,more preferably a nitride layer. The oxide layer and the nitride layermay be a single layer, multiple layers, or combinations thereof.

In addition, the oxide layer and the nitride layer may be a layerdeposited on an inner surface of the ring-shaped groove 30A or a layerobtained by oxidizing or nitriding a surface of the semiconductorsubstrate 1A which appears on the inner surface of the ring-shapedgroove 30A. With this insulating structure, a negative effect of theinorganic insulating layer 33A on the semiconductor substrate 1A can beblocked by the insulating layers 31A, 32A. For example, withstandvoltage failure of an oxide film due to an alkali metal (Na, K) whichmay be contained in the above glass material, p-n junction leakagefailure due to a transition metal (Fe, Cu, Zn), P-inversion failure dueto a group 3 element (B, Al) and so on can be avoided by the insulatinglayers 31A, 32A.

In the present embodiment, the insulating layers 31A, 32A are formed byoxidizing or nitriding inner wall surfaces of the ring-shaped groove30A. That is, the inner surfaces of the ring-shaped groove 30A arecovered with the insulating layers 31A, 32A, and the inorganicinsulating layer 33A fills the ring-shaped groove 30A covered with theinsulating layers 31A, 32A.

If the semiconductor substrate 1A is a common silicon substrate, forexample, the oxide layer is a silicon oxide layer and the nitride layeris a silicon nitride layer. The silicon oxide layer and the siliconnitride layer may be formed by applying a known technology. For example,there have been known a process of oxidizing or nitriding a surface of asilicon substrate and a process of depositing an insulating layer usinga chemical vapor deposition process (CVD process), and either processmay be employed. The oxidizing or nitriding depth of the insulatinglayers 31A, 32A, i.e., substantial layer thickness is preferablydetermined in view of actually required transmission characteristics.

Generally speaking, the silicon nitride layer is superior in insulatingcharacteristics to the silicon oxide layer. In addition, the nitridelayer has excellent chemical stability, electrical insulation, thermalshock resistance, and thermal deformation resistance. From a generalpoint of view, therefore, the insulating layers 31A, 32A are preferablycomprised of a silicon nitride layer.

Moreover, when the insulating layers 31A, 32A are comprised of a siliconnitride layer, they have excellent chemical stability, thermal shockresistance, and thermal deformation resistance. Accordingly, there canbe realized a separate insulating structure having excellent chemicalstability, thermal shock resistance, and thermal deformation resistance.

Referring to FIG. 3, semiconductor devices 7A are formed on one side ofthe semiconductor substrate 1A being a silicon substrate. The columnarconductor 2A penetrates the semiconductor substrate 1A along thethickness direction, and at its one end, a connection electrode 62A andan overlying electrode 61A for external connection are sequentiallyjoined together. The semiconductor devices 7A are connected to theconnection electrodes 62A through undepicted wiring. The semiconductordevices 7A and the connection electrodes 62A are covered with aninsulating film 4A provided on one side of the semiconductor substrate1A. On the other hand, an electrode 63A for external connection is alsoconnected to the other end of the columnar conductor 2A.

At least one of the connection electrodes 62A, 63A may be continuouswith the columnar conductor 2A as an integral part thereof. In FIG. 2,furthermore, an insulating resin is preferably filled into a gap betweenadjacent ones of the substrates SM1 to SMn, for example, between thesubstrates SM1 and SM2.

With reference to FIG. 5, next will be described an electronic devicecapable of preventing thermal deterioration which may occur when joiningthe columnar conductors between the substrates SM1 to SMn. Referring toFIG. 5, a connection conductor 4B includes a first electrode film 41B, asecond electrode film 42B, and a third electrode film 43B. The firstelectrode film 41B is a member for serving as a lead-out electrode for aconnection 6B and has a pattern for continuously covering the surface ofthe connection 6B and an insulating layer 2B. The second electrode film42B is disposed above the connection 6B and joined to the surface of thefirst electrode film 41B.

The third electrode film 43B is joined onto the second electrode film42B and the first electrode film 41B. The third electrode film 43B iscomprised of a noble metal film and serves as an antioxidizing film forflux-less joining. The noble metal film comprising the third electrodefilm 43B preferably contains at least one selected from the groupconsisting of Ag, Au, Pd and Pt. In addition, the noble metal filmpreferably has a film thickness of 100 (nm) or less. Within this range,its inherent antioxidizing effect can be exhibited while suppressingincrease of the film thickness with respect to an overall filmthickness.

It is obviously seen from FIG. 5 that between adjacent ones of theplurality of substrates SM1 to SMn, for example, between the substratesSM1 and SM2, the columnar conductor 2A of one substrate SM2 is connectedto the connection conductor 4B of the other substrate SM1 through ajunction film 5B.

The junction film 5B contains a first metal or alloy component and asecond metal or alloy component having a higher melting point than thefirst metal or alloy component, whereby a melting temperature is madehigher than the melting point of the first metal or alloy component.

With the above composition of the junction film 5B, when a heattreatment is performed for joining, the small size effect due to thesmall film thickness of the junction film 5B allows the second metal oralloy component to melt at a temperature close to the melting point ofthe first metal or alloy component. At this time, of course, the firstmetal or alloy component can also be melted. Then, since the first metalor a low melting point metal of the alloy component is consumed byreacting with the connection conductor 4B and forming an intermetalliccompound, the melting point increases considerably after joining.

In the electronic device being a finished product after solidification,moreover, since the melting temperature of the junction film 5B aftersolidification is mainly dominated by the melting point of the secondmetal or alloy component, the melting temperature of the junction film5B increases to a temperature close to the melting point of the secondmetal or alloy component, i.e., a temperature that is higher the meltingpoint of the first metal or alloy component at the very least.

According to the present invention, therefore, it is possible to realizea highly heat-resisting electronic device which requires a low heattreatment temperature during the joining process but can secure a highmelting point after solidification.

The first metal or alloy component preferably contains at least oneselected from the group consisting of Sn, In, Bi, Sb and Ga. On theother hand, the second metal or alloy component preferably contains atleast one selected from the group consisting of Cr, Cu, Ag, Au, Pt, Pd,Ni, a Ni—P alloy and a Ni—B alloy.

When manufacturing the electronic device of FIG. 5, between the adjacentsubstrates SM1 and SM2, the junction film 5B, which contains the firstmetal or alloy component and the second metal or alloy component havinga higher melting point, is formed on the connection conductor 4B of thesubstrate SM1, or the junction film 5B, which contains the first metalor alloy component and the second metal or alloy component, is formed onthe end face of the columnar conductor 2A of the substrate SM2.

Of course, the junction film 5B may be formed on both sides. The firstmetal or alloy component and the second metal or alloy component arecomprised of the above metal materials. The junction film 5B may beformed by applying a known film formation technology such as filmtransfer, printing, sputtering, and electron beam evaporation.

Then, the substrates SM1 and SM2 are stacked in alignment with eachother. Thus, only the junction film 5B lies between one end of thecolumnar conductor 2A of the substrate SM2 and the connection conductor4B of the substrate SM1. The junction film formation process and thealigning and stacking process are repeated according to the number ofrequired layers.

Then, the first metal or alloy component and the second metal or alloycomponent contained in the junction film 5B are melted by a heattreatment. In the melting process, the heat treatment is performed suchthat the already solidified columnar conductor 2A will not be meltedagain. Thereafter, the junction film is solidified by natural cooling orforced cooling. Thus, there is obtained the electronic device shown inFIGS. 1 and 2.

In the above heat treatment process, since the junction film 5B has amelting point reducing effect due to the small size effect of the filmthickness, the second metal or alloy component can be melted at atemperature lower than its melting point, along with the first metal oralloy component, thereby avoiding thermal damage to the connection 6Band so on.

After solidification, the melting temperature of the junction film 5Brises almost to the melting point of the second metal or alloycomponent. Thus, there is obtained a highly heat-resisting electronicdevice.

With the above results being further developed, needless to say, similareffects can be obtained even when metal balls whose surface is coatedwith the first metal or alloy, e.g., Cu or Ni balls, are used for thejunction film 5B. If combined, it will also be effective as a method forsecuring a space between wafers.

As already shown in FIG. 2, the electronic device according to thepresent invention may also include the interposer INT in addition to thesemiconductor substrates. FIG. 6 shows one embodiment of the interposer.In FIG. 6, the portions corresponding to the components shown in FIGS. 1to 5 are indicated by the same reference symbols to avoid duplicativeexplanation. The interposer differs from the substrates SM1 to SMn shownin FIGS. 1 to 5 in that it has no semiconductor device and is notnecessarily provided with the insulating film 4A and the connectionelectrodes 61A, 62A, 63A. However, at least one of the connectionelectrodes 62A, 63A may be continuous with the columnar conductor 2A asan integral part thereof.

Although not shown in the drawings, when manufacturing the electronicdevice shown in FIGS. 1 and 2, furthermore, the substrates SM1 to SMncan be efficiently stacked on the interposer INT such that the substrateSM1, which is previously formed with the columnar conductor 2A, isstacked and joined onto the interposer INT, an insulating resin isfilled into a gap formed between the interposer INT and the substrateSM1, and the surface of the substrate SM1 is then polished to expose anend face of the columnar conductor 2A, which is followed by repeatingthe steps of stacking and joining the next substrate SM2 and filling theinsulating resin into a gap formed between the substrate SM1 and thesubstrate SM2 and so on.

2. Conductive Composition

Next will be described a conductive composition suitable for forming thecolumnar conductor and the junction film in the electronic deviceaccording to the present invention. Referring to FIG. 7, a conductivecomposition according to the present invention includes first metalparticles 1D and second metal particles 2D.

The first metal particles 1D have an average particle size in such a nmrange as to exhibit small size effect, enabling melting at a temperaturelower than their melting point. In the present invention, the term “nmrange” refers to the range of 100 (nm) or less.

The second metal particles 2D have a melting point in such a range thattheir melting can be caused by melting of the first metal particles 1D.The first and second metal particles 1D, 2D may be a single crystal or apolycrystal. Preferably, the first and second metal particles 1D, 2D arespherical in shape.

In the present invention, since the first metal particles 1D have anaverage particle size in such a nm range as to exhibit small sizeeffect, enabling melting at a temperature lower than the melting pointof their material, it can be melted at a temperature lower than themelting point. Particularly when the particle size (average particlesize) of the first metal particles 1D is 20 (nm) or less, they exhibitthe quantum size effect and are therefore allowed to melt at atemperature that is considerably lower than a melting point of aconstituent material, for example, 250° C. or less, preferably, 200° C.or less, more preferably, 180° C. or less.

Specifically, the first metal particles 1D may be made of a materialcontaining at least one selected from the group consisting of Ag, Cu,Au, Pt, Ti, Zn, Al, Fe, Si and Ni. Here, the melting point of Ag is961.93°, the melting point of Cu is 1083.4° C., the melting point of Auis 1064.43° C., the melting point of Pt is 1769° C., the melting pointof Ti is 1660° C., the melting point of Zn is 419.58° C., the meltingpoint of Al is 660.4° C., the melting point of Fe is 1535° C., themelting point of Si is 1410° C., and the melting point of Ni is 1453° C.

Because of the quantum size effect, the first metal particles 1D made ofsuch a high melting point metal material are allowed to melt at atemperature of, for example, about 250° C., preferably, 200° C. or less.In order to obtain the junction structure, however, it is necessary toselect a metal component from the above group in view of the joiningability to an object to be joined.

The conductive composition according to the present invention includesnot only the first metal particles 1D but also the second metalparticles 2D. Melting of the first metal particles 1D causes melting ofthe second metal particles 2D. Thus, the second metal particles 2D canbe melted along with melting of the first metal particles 1D.

The second metal particles 2D may be made of a material that can melt ata reduced melting temperature of the first metal particles 1D.Specifically, such a material may be at least one selected from thegroup consisting of Sn, In and Bi. The melting point of Sn is 232° C.,the melting point of In is 156.61° C., and the melting point of Bi is271.3°. In view of the meltability, preferably, the second metalparticles 2D have an average particle size in the range of 1 to 300 μm.

If bismuth (Bi) is selected for the second metal particles 2D, a metalconductor without any cavities or voids within the minute space can beformed with the above metal filling apparatus by utilizing volumeexpansion characteristics during cooling.

In order to form an electrode such as a columnar conductor, a junctionfilm, and a wiring conductor pattern on a chip or wafer using theconductive composition according to the present invention, theconductive composition should be solidified after melting. At this time,the melting temperature decreases to a level considerably lower than themelting point of the first metal particles 1D, so that the columnarconductor, the junction film, or the wiring conductor pattern can beformed without causing thermal deterioration of a previously formedsemiconductor circuit element. For formation of the columnar conductor,use can be made of the apparatuses illustrated in FIGS. 30 to 42.

Although the first metal particles 1D are allowed to melt, for exampleat about 250°, this is because their melting point is considerablyreduced by the small size effect and the quantum size effect, and themelting point of the constituent metal material of the first metalparticles 1D is much higher than the actual melting temperature, asdescribed above. Accordingly, heat resistance due to the high meltingpoint of the first metal particles 1D can be secured aftersolidification. If the first metal particles 1D is made of at least oneselected from the group consisting of Ag, Cu, Au, Pt, Ti, Zn, Al, Fe, Siand Ni, for example, heat resistance due to the high melting point ofthese materials can be secured after solidification.

Although the compositional ratio of the first metal particles 1D to thesecond metal particles 2D varies depending on the selected materials,the effects of the present invention can be obtained as long as theratio of the first metal particles 1D to the total (weight) of the firstmetal particles 1D and the second metal particles 2D is in the range of1 to 50% by weight.

The conductive composition according to the present invention may beused as it is in the form of a powder where the first metal particles 1Dand the second metal particles 2D are mixed together, or may be used inthe form of a conductive paste where the powder is mixed with an organicvehicle.

The metal particles according to the present invention may bemanufactured by a commonly known nanoparticle production process. Forexample, they may be manufactured by a crushing process where a mass ofmaterial is crushed to a nanometer-size using a ball mill or jet mill,an aggregation or reduction process where an ion or complex being amaterial is reduced by a reducing agent or electrochemically andaggregated into nanoparticles, a thermal decomposition process where amaterial is thermally decomposed as it is or while being supported by acarrier, a physical vapor deposition (PVD) process such as a gasevaporation process, a laser evaporation process where rapid evaporationis caused by laser, and a chemical vapor deposition (CVD) process wherechemical reaction is brought about in a gaseous phase.

In addition to the above common production processes, it may also bemanufactured by a centrifugal granulation process. According to thecentrifugal granulation process, under an argon inert gas atmosphere,there are carried out the steps of supplying a molten metal or alloybeing a material of the first or second metal particles onto ahigh-speed rotating dish disk, spattering it into droplets by the actionof a centrifugal force, and rapidly cooling them into sphericalparticles by contact with the gas atmosphere.

In the granulation process, the molten material is self-assembled duringthe rapid cooling and solidification, resulting in a composite structureof crystals or amorphous bodies.

The term “composite structure” as used herein refers to a structure inwhich individual microcrystals are separated from each other byscattered materials or voids. The spherical particles are aggregates ofdifferent crystals or amorphous bodies. On the other hand, the term“self-assembling” refers to formation of a composite structure due toaggregation of constituent crystals or amorphous bodies in the processof supplying a molten material onto a high-speed rotating dish disk,spattering it into droplets by the action of a centrifugal force, andrapidly cooling and solidifying them into spherical particles.

According to the centrifugal granulation process, typically, there areobtained metal particles in the range of 1 to 300 μm, which satisfiesthe average particle size of the second metal particles 2D. In order toobtain much smaller particles, the metal particles obtained by thecentrifugal granulation process may be decomposed by a plasma treatmentand again subjected to the centrifugal granulation process. Thisprovides spherical ultrafine particles which satisfy the averageparticle size of the first metal particles 1D.

The conductive composition according to the present invention may becontained as a filling material in a molten metal MC of the above metalfilling apparatus or may be used as an electrode material for formingwiring patterns on a substrate surface. If the electronic device is athree-dimensional system-in-package (3D-SiP), furthermore, it may alsobe used as a junction material for joining electrodes formed on stackedsubstrates.

As described above, since the conductive composition according to thepresent invention can be melted at a low temperature and secure a highmelting point after solidification, regardless of which one of theelectrode material, the filling material and the junction material isits application, it is possible to realize a highly reliable electronicdevice.

3. Columnar Conductor (Equiaxed Crystallization)

Next will be described equiaxed crystallization of the columnarconductor that is suitable for preventing the occurrence of cracking inthe above columnar conductor or the insulating film disposed between thecolumnar conductor and the through-hole.

FIG. 8 shows one embodiment of a substrate to be used for an electronicdevice according to the present invention. A columnar conductor 3E ismade of a metal or alloy and fills a minute space 30E extending from onesurface of a substrate 1E along a thickness direction. Such a structurecan be obtained, for example, by a metal filling apparatus that willdescribed later.

One end of the columnar conductor 3E is opposed to a surface of a bottomlayer 2E closing the bottom of the minute space 30E. The bottom layer 2Emay be any one of a conductor, an insulator, and a semiconductor, butwill be described here as a thin-film conductor.

Although FIG. 8 shows a substrate of a simple structure, it may actuallyhave a more complicated structure in order to realize appropriatefunction and structure depending on the type of the electronic device.The substrate may be a wafer or a chip cut out of the wafer. Moreover,it may be a single layer substrate or a multilayer substrate in which aplurality of layers are stacked.

For the substrate 1E, various materials may be used as long as having acertain heat resistance, including a metal, an alloy, a metal oxide, aceramic, a glass, a plastic, a composite thereof, and a laminatethereof. The physical properties and structure of the substrate 1E varydepending on the type of the target device.

For a semiconductor device, for example, use can be made of Si, SiC, SOIor the like. For a passive electronic circuit device, it may take theform of a dielectric, a magnetic or a composite thereof. Also whenrealizing a MRAM (magnetoresistive random access memory), a MEMS (microelectro mechanical systems), an optical device, a solar cell, a flatdisplay such as an EL display, a liquid crystal display, or a plasmadisplay, a wafer to be used should have physical properties andstructure meeting the requirements. If the substrate 1E is asemiconductor substrate, it is possible to previously form asemiconductor circuit element.

The bottom layer 2E is formed on one side of the substrate 1E. If thesubstrate 1E is a semiconductor wafer and a semiconductor circuitelement is formed previously, the bottom layer 2E may serve as anelectrode for the semiconductor circuit element. In this case, thebottom layer 2E may have various planar patterns depending on requiredfunctions. If needed, the area around the bottom layer 2E may be filledwith an insulating film.

The bottom layer 2E is made of a known material such as a metal materialmainly composed of Cu. If needed, it may contain Zn (zinc), Al(aluminum) or Ti (titanium). The bottom layer 2E may be formed by athin-film formation technology such as CVD or sputtering.

Although the present embodiment illustrates the case where a singlecolumnar conductor 3E is provided for a single bottom layer 2E, itshould not be construed as limited thereto. It is also possible toprovide a plurality of columnar conductors 3E for a single bottom layer2E. The minute space 30E is a through-hole or a non-through-hole (blindhole) as described above.

The columnar conductor 3E is made of a melt-processed metal and has anarea of an equiaxed crystal 31E at an area opposed to the substrate 1E,as shown in FIG. 9 on an enlarged scale. The equiaxed crystal 31E areamay be distributed entirely over the columnar conductor 3E or partiallyor entirely over a peripheral area of the columnar conductor 3E opposedto the substrate 1E. With the columnar conductor 3E having the equiaxedcrystal 31E area, there can be obtained a highly reliable, high qualitysubstrate which hardly causes cracking of the columnar conductor 3E,cracking of the substrate 1E or breaking of the insulating film.

Using the macrostructure theory about the melt-processed metal, thereason can be explained as follows. When forming the columnar conductor3E by melt-processing, specifically, the hole-like minute space 30Eformed in the substrate 1E is used as a mold, as shown in FIG. 10, and amolten metal ME is then filled into it and solidified, as shown in FIG.11. At this time, three structural areas of a chill layer, a columnarcrystal and an equiaxed crystal can be assumed as a general form of acrystal grain that will be generated upon solidification of the moltenmetal ME. The columnar crystal is a crystal zone arrayed and elongatedin parallel to the direction of heat flow. The equiaxed crystal is auniform isometric crystal area and has isotropy. The equiaxed crystalhas a smaller crystal grain size than the chill layer.

In this case, the most important factor determining the materialproperties of the columnar conductor 3E obtained by solidifying themolten metal ME is a relative ratio of the columnar crystal zone to theequiaxed crystal area. If the columnar conductor 3E obtained bysolidification has only a columnar crystal 32E and a chill layer 33Ewithout any equiaxed crystal area, as shown in FIG. 12, impuritieshaving solid solubility and impurities having no solid solubility in themolten metal are concentrated at an area where structures of thecolumnar crystal 32E collide with each other, causing severesegregation. In addition, the columnar crystal 32E inherently grows intoa large grain. Accordingly, a grain boundary 34E easily serves as apropagation path of cracking, causing cracking of the columnar conductor3E and cracking of the substrate 1E, as schematically shown in FIG. 13.In the case where an insulating film is put on an inner surface of theminute space 30E (which will be described later), the insulating filmmay be broken by the large grain growth of the columnar crystalstructure.

To the contrary, since the equiaxed crystal structure is isotropic andhas a small grain size, it does not cause segregation easily unlike thecase of the columnar crystal. In the present invention, since thecolumnar conductor 3E has the equiaxed crystal 31E area at least in anarea opposed to the substrate 1E, there is obtained the isotropy due tothe equiaxed crystal structure. This suppresses the occurrence ofcracking of the conductor, breaking of the insulating film, and crackingof the substrate.

At least in a peripheral surface area opposed to the substrate 1E,preferably, the equiaxed crystal area accounts for a larger area of thecolumnar conductor 3E than the columnar crystal area. With thisrelationship, the isotropy of the equiaxed crystal becomes morepredominant at least in the area opposed to the substrate 1E, whichsuppresses more effectively cracking of the conductor, breaking of theinsulating film, and cracking of the substrate.

In order to develop the equiaxed crystal structure, it is necessary tosuppress the growth of the columnar crystal, which can be achieved byarranging the condition suitable for nucleation of the equiaxed crystal.The necessary condition is such that a crystal network structure has tobe formed within the molten metal as an obstacle which prevents thegrowth of the columnar crystal. As such means, the following two methodsare known.

(a) Control melt-processing conditions and use an inoculant(b) Apply mechanical or ultrasonic vibration to induce dynamic grainrefinement

In the present invention, the above methods (a) and (b) may be usedeither alone or in combination with each other. In the case of choosingthe method (a), it has been found that gallium (Ga) or bismuth (Bi),which has a negative volume change, is effective as an inoculant. Inaddition, use can be made of indium (In). For the molten metal, use canbe made of metal elements commonly used for formation of such aconductor. Examples include Sn, Cu, Ag, Al and Au. Since preferredvalues of composition ratio of these metals to the inoculant varydepending on the type of a selected metal and temperature, pressure andso on during the melt-processing, they are preferably determinedempirically and experimentally. However, the equiaxed crystal is notnecessarily required to be formed by melt-processing. Other possiblemeans may be used, if any.

When forming the columnar conductor 3E by melt-processing, use can bemade of, but not limited to, composite spherical particles having aparticle size of 1 μm or less and an internal crystal structure of 200nm or less.

FIG. 14 is a SEM photograph of a substrate according to the presentinvention, while FIG. 15 is a SEM photograph of a substrate being acomparative example to which the present invention was not applied, andin either case, the columnar conductor 3E filled the minute space 30Ebored into the substrate 1E. In FIGS. 14 and 15, the columnar conductors3E had the same main component but differed from each other in thatbismuth (Bi) was contained as an inoculant in FIG. 14 but bismuth (Bi)was not contained in FIG. 15. As described above, bismuth (Bi) may bereplaced by gallium (Ga) or indium (In).

It is apparent from the comparison of FIG. 14 with FIG. 15 that in thesubstrate of FIG. 15, the columnar conductor 3E has many elongatedcrystals representing columnar crystals, but in the substrate of FIG. 14according to the present invention, the columnar conductor 3E has finecrystals representing equiaxed crystals. The equiaxed crystal structureof FIG. 14 suppresses the occurrence of cracking of the conductor,breaking of the insulating film, and cracking of the substrate, whichwould become a problem in the columnar crystal structure of FIG. 15.

FIG. 16 shows another embodiment of a substrate according to the presentinvention. In this figure, the components corresponding to thecomponents shown in FIG. 8 are indicated by the same reference symbolsto avoid duplicative explanation. The present embodiment ischaracterized in that a foundation layer 4E for serving as a junctionfilm is joined to almost the entire peripheral surface of the columnarconductor 3E within the minute space 30E. The foundation layer 4E may beformed by a thin-film formation technology such as sputtering.

Also in the embodiment of FIG. 16, the columnar conductor 3E is made ofa metal or alloy and has an equiaxed crystal area at least in aperipheral area opposed to the foundation layer 4E. This avoids theproblem that cracking of the columnar conductor 3E, the foundation layer4E or the substrate 1E is caused by the grain growth of the columnarcrystal structure.

When forming the columnar conductor 3E by melt-processing, moreover,metal materials capable of forming an intermetallic compound may beselectively used as a metal component for forming the columnar conductor3E and the foundation layer 4E, so that these 3E, 4E can be firmlyjoined together with the intermetallic compound.

4. Junction Structure Between Columnar Conductor and Other Conductors

Next will be described preferred embodiments of the junction structurebetween the columnar conductor and other conductors.

(1) First Embodiment

Referring to FIG. 17, a columnar conductor 3 fills a minute space 30extending along the thickness direction from one surface of a substrate1. At the bottom of the minute space 30, one end of the columnarconductor 3 is opposed to a film surface of a first conductor 2 across ajunction film 4.

Although FIG. 17 illustrates the case where a single columnar conductor3 is provided for a single first conductor 2, it should not be construedas limited thereto. It is also possible to provide a plurality ofcolumnar conductors 3 for a single first conductor 2.

The minute space 30 filled with the columnar conductor 3 is athrough-hole, a non-through-hole (blind hole), or a via hole. While theminute space 30 has a hole diameter of, for example, 60 μm or less, thethickness of the wafer itself is typically tens of μm. Accordingly, theminute space 30 has a considerably high aspect ratio.

Referring to FIG. 17, the first conductor 2 is formed flat on thesurface of the substrate 1, and the second conductor 3 is deposited onthe surface of the first conductor 2 with the junction film 4 between.That is, the conductors are arranged two-dimensionally.

Although FIG. 17 shows a substrate of a simple structure, it mayactually have a more complicated structure in order to realizeappropriate function and structure depending on the type of theelectronic device, for example, as shown in FIGS. 1 to 5. The substratemay be a wafer or a chip cut out of the wafer.

For the substrate 1, various materials may be used as long as having acertain heat resistance, including a metal, an alloy, a metal oxide, aceramic, a glass, a plastic, a composite thereof, and a laminatethereof. The physical properties and structure of the substrate 1 varydepending on the type of the target device. For a semiconductor device,for example, use can be made of Si, SiC, SOI or the like. For a passiveelectronic circuit device, it may take the form of a dielectric, amagnetic or a composite thereof. Also when realizing a MRAM(magnetoresistive random access memory), a MEMS (micro electromechanical systems), an optical device, a solar cell, a flat displaysuch as an EL display, a liquid crystal display, or a plasma display, awafer to be used should have physical properties and structure meetingthe requirements. If the substrate 1 is a semiconductor substrate, it ispossible to previously form a semiconductor circuit element.

The first conductor 2 is a flat thin film formed on one side of thesubstrate 1. If the substrate 1 is a silicon wafer and the semiconductorcircuit element is formed previously, the first conductor 2 may serve asa lead conductor for the semiconductor circuit element. The firstconductor 2 may have various planar patterns depending on requiredfunctions. If needed, the area around the first conductor 2 may befilled with an insulating film. The first conductor 2 is made of a knownmaterial such as a metal material mainly composed of Cu. If needed, itmay contain Zn (zinc), Al (aluminum) or Ti (titanium). The firstconductor 2 may be formed by a thin-film formation technology such asCVD or sputtering.

The second conductor 3 is made of a metal material mainly composed of aSn alloy. Specifically, it may contain Sn and at least one of In, Al andBi. It may further contain Ga, which is useful as an antioxidizingagent. The illustrated second conductor 3 is a flat thin film depositedon the surface of the first conductor 2 with the junction film 4between.

The junction film 4 is made of a metal material having a higher meltingpoint than the Sn alloy and disposed at least between the firstconductor 2 and the second conductor 3 for joining them together,wherein the metal element is diffused into the second conductor 3 toproduce an alloy area AL. The metal element is diffused with such aconcentration gradient that its content (diffusion amount) decreaseswith the distance from the junction film 4, as schematically shown inFIG. 17. In FIG. 17, the alloy area AL is shown as if it is an areadefined by the alternate long and short dash line, but this is merelyfor convenience of description. Actually, there is no definite boundary.For the junction film 4, use can be made of any metal having a highermelting point than the Sn alloy. Specifically, examples include Cu, Ag,Al, Au and Zn.

(Manufacturing Method)

Next will be described a method for manufacturing the above electronicdevice, particularly, a substrate or interposer to be used for theelectronic device.

With chemical reaction etching, for example, using an inductivelycoupled high density plasma apparatus, or laser drilling, at first, theminute space 30 is formed by etching along the thickness direction ofthe substrate 1, as shown in FIG. 18. The shape of the minute space 30varies depending on the characteristics of the chemical reaction etchingand is not limited to the illustrated one.

Then, metal particles 40 are supplied to the inside of the minute space30, for example, by means of screen printing. Specific examples of themetal particles 40 are the same as described above. The metal particles40 may be supplied in such a small quantity as to form only one to threelayers of metal particles on the surface of the first conductor 2.

Then, the columnar conductor 3 is formed by pouring into the minutespace 30 a molten metal M containing the Sn alloy, as shown in FIG. 19.During this molten metal pouring process, the metal particles 40 withinthe minute space 30 are melted and diffused into the molten metal Mcontaining the Sn alloy. By cooling and hardening, then, the junctionfilm 4 is formed between the first conductor 2 and the columnarconductor 3 for joining them together, wherein the metal element withinthe junction film 4 is diffused into the columnar conductor 3 to createthe alloy area AL (see FIG. 17). For filling, pressurizing and hardeningthe molten metal M, use can be made of the following apparatusesillustrated in FIGS. 30 to 42.

Next, the effects of the above manufacturing method will be described indetail with reference to the experimental data of FIGS. 20 to 24 and incomparison with a conventional substrate (which may also be referred toas electronic device). FIG. 20 is a SEM photograph of a conventionalsubstrate being a comparative example, and FIG. 21 shows the SEMphotograph of FIG. 20 on an enlarged scale. FIG. 22 is a SEM photographof a substrate according to the present invention, FIG. 23 shows the SEMphotograph of FIG. 22 on an enlarged scale, and FIG. 24 shows the SEMphotograph of FIG. 22 on a further enlarged scale.

The substrate shown in FIGS. 20 and 21 is constructed such that thefirst conductor 2 mainly composed of Cu was formed on one side of thesilicon substrate 1 and one end of the columnar conductor 3 was directlyjoined to the first conductor 2. The columnar conductor 3 was formed byfilling a molten electrode material mainly composed of a molten Sn alloyinto the minute space 30, wherein a flux was used for reducing the oxidefilm on the surface of the first conductor 2.

As apparent from FIGS. 20 and 21, considerably large voids are formedbetween the periphery of the columnar conductor 3 and the inner wallsurface of the minute space 30. Although the oxide film on the surfaceof the first conductor 2 can be reduced by applying a flux reductiontechnology, pouring the flux into the minute space 30 along with themolten metal material generates a flux gas. In electronic devices ofthis type, the minute space 30 is a minute hole having a hole diameterof, for example, tens of μm or less and also a considerably high aspectratio. If the flux gas is generated within the thus-shaped minute space30, of course, the gas cannot easily escape. This creates voids due tothe flux gas around the columnar conductor 3, which results in reductionof sectional area of the columnar conductor 3, increase of electricalresistance, and eventually poor connection to the first conductor 2 andincrease of junction resistance.

In the substrate according to the present invention, on the other hand,the peripheral surface of the columnar conductor 3 is in close contactwith the inner wall surface of the minute space 30 formed in thesubstrate 1, so that there is almost no voids between them, as shown inFIGS. 22 to 24. Although a shadow like a void can be seen at a contactsurface between the first conductor 2 and the columnar conductor 3, thisis not a void but a break caused by polishing before taking the SEMphotograph.

(2) Second Embodiment

FIG. 25 is a view showing another embodiment of a substrate to be usedfor an electronic device according to the present invention. The presentembodiment is characterized in that the junction film 4 is joined toalmost the entire peripheral surface of the columnar conductor 3 withinthe minute space 30. The junction film 4 may be formed by a thin-filmformation technology such as sputtering.

In the embodiment shown in FIG. 25, since the metal element contained inthe junction film 4 is diffused into the columnar conductor 3 to createthe alloy area AL over the entire peripheral surface of the columnarconductor 3, mutual junction strengths between the first conductor 2,the columnar conductor 3 and the substrate 1 can be further increased incomparison with the embodiment shown in FIG. 17.

Next will be described a method for manufacturing the substrate shown inFIG. 25.

A. Manufacturing Method 1

For example, after the minute space 30 is formed by etching along thethickness direction of the substrate 1 with chemical reaction etching,for example, using an inductively coupled high density plasma apparatus,or laser drilling, the junction film 4 is deposited on the inner wallsurface of the minute space 30 and the surface of the substrate 1, asshown in FIG. 26. The junction film 4 may be formed by sputteringdeposition.

Then, as shown in FIG. 27, the molten metal M containing the Sn alloy issupplied to the space surrounded by the junction film 4 deposited on theinner wall surface of the minute space 30. Thereafter, the substrate ofFIG. 25 according to the present invention can be obtained by coolingand hardening the molten metal M. For filling, pressurizing andhardening the molten metal M, use can be made of the followingapparatuses illustrated in FIGS. 30 to 42.

The process of forming the junction film 4 on the inner wall surface ofthe minute space 30 of the substrate 1 is also applicable to the case ofplating, but in the present invention, as described above, the columnarconductor 3 is formed by pouring into the minute space 30 the moltenmetal M containing the Sn alloy, instead of plating. As compared withthe plating deposition process, the number of processing steps and theprocessing time can be decreased considerably in the process ofsupplying the molten metal M. As compared with the case of a platingtechnology, therefore, the number of processing steps and the processingtime can be decreased and shortened considerably. Accordingly, there canbe realized a low-cost three-dimensional arrangement substrate.

B. Manufacturing Method 2

The substrate shown in FIG. 25 can also be manufactured by the processshown in FIGS. 28 and 29. At first, after a thin metal sheet 42 isplaced on one side of the substrate 1 which has an opening of the minutespace 30 formed by chemical reaction etching, for example, using aninductively coupled high density plasma apparatus, or laser drilling, asshown in FIG. 28, the molten metal M is supplied onto the thin metalsheet 42, as shown in FIG. 29. With the molten metal M being supplied,the metal element contained in the thin metal sheet 42 is diffused intothe Sn alloy of the molten metal M to create the alloy area. Bysubsequently cooling and hardening the molten metal M, there is obtaineda substrate where the junction film 4 is joined to almost the entireperipheral surface of the columnar conductor 3 within the minute space30, as shown in FIG. 25. For filling, pressurizing and hardening themolten metal M, use can also be made of the following apparatusesillustrated in FIGS. 30 to 42.

5. Molten Metal Filling Apparatus

In a broad sense, the molten metal filling apparatus according to thepresent invention refers to the one for filling a molten material into aminute space of a target material and then hardening it. In theproduction of the electronic device shown in FIGS. 1 to 6, which is theactual application, it is suitable for filling of the columnar conductor2A. However, it may also be used for filling of the insulating layer33A.

In the embodiment shown in FIG. 30, a target 2C is a thin substrate suchas a wafer for an electronic device (semiconductor device), but it canbe widely used without limitation and is also applicable to the casewhere a minute conductor filled structure, a junction structure or afunctional portion is formed within another electronic device ormicromachine, for example.

For the target 2C, various materials may be used as long as having aresistance to heat emitted from the molten metal, including a metal, analloy, a metal oxide, a ceramic, a glass, a plastic, a compositethereof, and a laminate thereof. Moreover, the whole shape of the target2C is not limited to the illustrated flat panel shape but may take anyshape.

If a wafer is chosen as the target 2C, its physical properties andstructure vary depending on the type of the target device. For asemiconductor device, for example, use can be made of a Si wafer, a SiCwafer, a SOI wafer or the like. For a passive electronic circuit device,it may take the form of a dielectric, a magnetic or a composite thereof.Also when manufacturing a MRAM (magnetoresistive random access memory),a MEMS (micro electro mechanical systems), or an optical device, a waferto be used should have physical properties and structure meeting therequirements.

The minute space in the wafer is generally called “through-hole”,“non-through-hole (blind hole)”, or “via hole”. The minute space has ahole diameter of, for example, 10 to 60 (μm). The thickness of the waferitself is typically tens of (μm). Accordingly, the minute space has aconsiderably high aspect ratio. This is a big reason why a problemoccurs when filling the molten metal MC into the minute space.

The metal filling apparatus comprises a support 1C, a molten metalsupply unit 12C, and a pressure control unit 13C. The support 1Cincludes a processing chamber AC for processing a wafer being the target2C, a first member 10C with a mounting surface for mounting of thewafer, and a second member 11C with a metal supply path 111C leading tothe processing chamber AC.

With one opening H1C of a minute space 21C being kept open, the firstmember 10C supports the target 2C from the side opposite from theopening H1C, as shown in FIG. 32. That is, the target 2C is placed onone side of the first member 10C. In the present embodiment, the minutespace 21C is a through-hole and an opening H2C on the side opposite fromthe opening H1C is closed by the first member 10C.

Although the minute spaces 21C have to be exposed, at least at oneopening H1C, to the atmosphere of the processing chamber AC, theiropening shape, path, number and so on may be determined arbitrarily.They are not required to be a through-hole as in the present embodimentbut may be a non-through-hole. They may also have a complicated shapenot only extending in the vertical direction as in the drawings but alsoconnecting together in a transverse direction perpendicular thereto. Theminute spaces 21C are not limited to intentionally formed ones but alsoinclude accidentally generated ones.

On the other hand, the second member 11C is combined with the firstmember 10C from the side of the exposed openings H1C, defining theprocessing chamber AC for the target 2C. Here, the combination may be amale-female fit as in the present embodiment or another fit, but it isdesirable that the processing chamber AC is formed between the secondmember 11C and the first member 10C with a higher airtightness.

The molten metal supply unit 12C supplies the molten metal MC to theprocessing chamber AC. The molten metal supply unit 12C has a meltingbath and is connected to the metal supply path 111C of the second member11C through a delivery pipe P1C. The metal supply path 111C leads to theprocessing chamber AC. In addition, the delivery pipe P1C is providedwith a valve C1C. When supplying the molten metal MC, the valve C1C isopened by mechanical control or manually.

FIG. 31 shows a state where the molten metal is supplied to theprocessing chamber AC. The molten metal MC is supplied by the moltenmetal supply unit 12C to fill up the processing chamber AC.

For example, the molten metal supply unit 12C can melt the metal withinthe range of 200 to 300° C. This melting temperature can be adjusted orreduced by selecting a combination of metal components and nano-sizingthem, as will be described below.

If the bottom of the minute space 21C is closed by the conductor,furthermore, it is also effective that noble metal nanoparticles aresupplied into the minute space 21C before pouring of the molten metal Mand subsequently the process of pouring the molten metal M is carriedout. With this process, an oxide film which may possibly be formed onthe conductor can be reduced by catalysis of the noble metalnanoparticles, so that a low electrical resistance junction can beformed between the molten metal MC and the conductor.

The noble metal may include gold (Au), silver (Ag), platinum (Pt),palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and osmium(Os). Among these elements, it preferably contains at least one selectedfrom the group consisting of gold (Au), platinum (Pt) and palladium(Pd).

The pressure control unit 13C controls the pressure within theprocessing chamber AC. When reducing the pressure, the pressure controlunit 13C reduces the pressure within the processing chamber AC, forexample, to a level as low as a degree of vacuum of 10⁻³ (Pa). Whenincreasing the pressure, on the other hand, an inactive gas such as N²gas is supplied to increase the gas pressure while preventing theoxidization of the molten metal material. The gas pressure within theprocessing chamber AC may be set, for example, within the range of 0.6to 1 (kgf/cm²). A suitable dynamic pressure can be generated bycontrolling the pressure rise/time characteristics before reaching theabove gas pressure.

Through a control pipe P2C, the pressure control unit 13C is connectedto a pressure transmission path 112C of the second member 11C. Thepressure transmission path 112C leads to the processing chamber AC.

In addition, the control pipe P2C is provided with a valve C2C. Whenincreasing or reducing the pressure within the processing chamber AC,the valve C2C is opened by mechanical control or manually.

Before the molten metal supply unit 12C supplies the molten metal MC,the pressure control unit 13C reduces the pressure within the processingchamber AC. This enables the above-mentioned differential pressurefilling.

The metal filling apparatus has a pressurizing means 14C for applying apressure to the processing chamber AC until the molten metal MC ishardened by cooling after the molten metal MC is filled into the minutespace 21C. The pressurizing means 14C applies at least one pressingforce selected from the group consisting of a gas pressure, a pressingpressure, an injection pressure, and a rolling pressure.

As the above pressurizing means 14C, use can be made of a press forapplying the pressing pressure, or the above pressure control unit 13Cmay double as the pressurizing means for applying the gas pressure. If aroller mechanism is provided on the inner surface side of the secondmember 11C, alternatively, the rolling pressure can be utilized. Controlof pressing time with such a pressurizing means may be performed eithermanually or mechanically.

When using the pressing pressure, the pressurizing means 14C isconnected to the second member 11C through a pressing shaft 15C of thepress, and after the minute space 21C is filled with the molten metalMC, the second member 11C is pushed toward the target 2C by applying thepressing pressure to the second member 11C. Thus, the molten metal MCcan be sufficiently filled into the minute space 21C down to the bottomthereof.

Next will be described the effects of the metal filling apparatusaccording to the present invention. FIGS. 32 to 36 are enlarged views ofan area about the target 2C in FIG. 30, showing the process of fillingthe molten metal MC into the minute space 21C.

As shown in FIG. 32, the target 2C is set on the first member 10C, andthen the second member 11C is combined with the first member 10C tocover the target 2C. This operation may be performed either manually ormechanically. Thus, the processing chamber AC is formed around thetarget 2C.

After setting, the valve C2C is opened to let the pressure control unit13C reduce the pressure within the processing chamber AC. After reducingthe pressure, the valve C2C is closed.

Then, as shown in FIG. 33, the molten metal MC is supplied from themolten metal supply unit 12C by opening the valve C1C. At this time,since the pressure within the processing chamber AC is previouslyreduced, the molten metal MC is filled by the differential pressure.Thus, the molten metal M can also be filled into the minute space 21Cthrough the opening H1C.

At this time, since the processing chamber AC is formed in the shape ofa thin sheet on a plane including the openings H1C, the molten metalsupply unit can supply the molten metal MC in such a manner as to form athin metal film FC over the openings H1C.

Then, as shown in FIG. 34, the filled molten metal MC is cooled andhardened by natural cooling or a forced cooling means such as liquidnitrogen or liquid helium. At this time, the above pressurizing meansapplies a pressure PC to the molten metal MC until it is hardened. Thus,the molten metal MC can be sufficiently filled into the minute space 21Cdown to the bottom thereof.

Finally, the thin metal film FC is remelted by a heating means 16C suchas a heater, as shown in FIG. 35, and the remelted thin metal film FC iswiped off by a metal film removing means such as a squeegee 17C, asshown in FIG. 36. With this subsequent processing, the surface of thetarget 2C can be flattened.

Moreover, what is needed is such a simple process as wiping off andtherefore resupply of the molten metal MC after cooling the molten metalor a CMP process is not required unlike the prior art, which contributesto simplification of the process and improved yield. If necessary,another process of repressurizing and then cooling may be furtherperformed according to the hardening process. However, the subsequentprocessing is merely for removing the thin metal film FC and flatteningone surface of the target 2C and therefore may be omitted if flatteningis not necessary.

Although heat for remelting is also conducted to a hardened metal GChardened within the minute space 21C, since the hardened metal GC has aconsiderably higher heat capacity than the thin metal film FC, remeltingof the thin metal film FC will never lead to remelting of the hardenedmetal GC. Thus, it is possible to wipe off only the thin metal film FC.Alternatively, the thin metal film FC may be mechanically removedwithout remelting.

Next, the effects of the present invention will be described withreference to the SEM (scanning electron microscope) photographs. FIG. 37is a sectional SEM photograph of a semiconductor wafer (silicon wafer)obtained without pressurized cooling, and FIG. 38 is a sectional SEMphotograph of a semiconductor wafer (silicon wafer) obtained withpressurized cooling.

Referring first to the SEM photograph of FIG. 37, a recess X1C is formedat the upper end of the hardened metal GC filling the minute space 21Cof the target wafer 2C, while a void X2C not filled with the hardenedmetal GC is also formed at the bottom. Other voids can also be foundbetween the periphery of the hardened metal GC and the inner surface ofthe minute space 21C.

Referring to the SEM photograph of FIG. 38, on the other hand, the upperend surface of the hardened metal GC filling the minute space 21C of thewafer 2C is a flat surface continuing to the upper surface of the wafer2C, and no recess can be found. The lower end surface of the hardenedmetal GC is in close contact with the bottom of the minute space 21C,and no void can be found at the bottom. Furthermore, the peripheralsurface of the hardened metal GC is in close contact with the innersurface of the minute space 21C, and no void can be found.

Here, the conditions with which the results shown in FIGS. 37 and 38were obtained are shown below.

Pressure within Processing Chamber during Pressure Reduction: 10⁻³ (Pa)Target: 300 (mm)×50 (μm) Silicon Wafer with Glass Protection Film

Dimension of Minute Space:

Opening Diameter of 15 (μm)

Bottom Hole Diameter of 10 (μm)

Composition of Molten Metal: Sn, In, Cu, Bi Melting Temperature ofMolten Metal: 250 (° C.)

Pressing Pressure during Pressurized Cooling: 2.0 (kgf/cm²)

Melting Temperature for Remelting: 250 (° C.)

Pressure for Repressurizing: 2.0 (kgf/cm²)

With the metal filling apparatus according to the present invention, ashas been described above, the target 2C can be held within theprocessing chamber AC between the first member 10C and the second member11C, wherein one opening H1C of the minute space 21C in the target 2C isexposed. Then, after the pressure within the processing chamber AC isreduced by the pressure control unit 13C, the molten metal MC issupplied to the processing chamber AC by the molten metal supply unit12C, whereby the molten metal MC is filled into the minute space 21Cthrough the exposed opening H1C by the differential pressure.

After filling, since the pressure PC is applied to the processingchamber AC by the pressurizing means until the molten metal MC ishardened by cooling, the molten metal MC within the minute space 21C ofthe target 2C put in the processing chamber AC is also pressurizedduring that time.

Thus, the molten metal MC can be sufficiently filled into the minutespace 21C down to the bottom thereof and deformation of the metal due tothermal contraction can be suppressed. Accordingly, the minute space 21Ccan be filled with the metal without creating any cavities or voids.

In the case where the minute space 21C is a through-hole, moreover,since the first member 10C supports the target 2C from the side oppositefrom the opening H1C of the minute space 21C, which is exposed to theprocessing chamber AC, the other opening H2C of the target 2C, which ison the side to be supported, can be closed. Therefore, the molten metalMC within the minute space 21C can be sufficiently pushed into theminute space 21C with the pressure PC being applied in one directionfrom the exposed opening H1C, while the molten metal is prevented fromleaking from the other closed opening H2C.

Also in the case where the minute space 21C is a non-through-hole,needless to say, the pressure can be similarly applied in one directionfrom the opening H1C without causing leakage of the molten metal MC.

Accordingly, the metal filling apparatus according to the presentinvention can also prevents the molten metal MC from having a recessedsurface which would otherwise be caused by cooling in the minute gap21C. This reliably secures electrical continuity to the outside.

Since the metal is prevented from having a recessed surface, moreover,resupply of a molten metal or a CMP process is not necessary aftercooling, which contributes to simplification of the process and improvedyield.

In the metal filling apparatus according to the present invention,furthermore, the processing chamber AC for holding the target 2C iscreated by combining the first member 10C and the second member 11C,while the molten metal supply unit 12C and the pressure control unit 13Care provided separately and independently. Accordingly, the metalfilling apparatus according to the present invention does not have theabove conventional complicated structure and in addition can save thelabor required for the formation and mounting of a metal sheet beforefilling the metal. With the metal filling apparatus according to thepresent invention, therefore, cost reduction and improvement ofprocessing efficiency can be achieved.

Next will be described another embodiment with reference to FIGS. 39 and40. Here, the components common to the foregoing embodiment areindicated by the same reference symbols to avoid explanation.

The difference between the present embodiment and the foregoingembodiment resides in the supply means of the molten metal MC. A moltenmetal supply unit 18C of the present embodiment is an injection machineusing screw extrusion, comprising a generally cylindrical barrel 181C, ascrew 182C rotatably mounted within the barrel 181C, a motor m1Cconnected to the upper end surface of the screw 182C for rotationallydriving it, and a hopper 183C for retaining the molten metal MC andsupplying it into the barrel 181C.

The barrel 181C is connected at the lower end to the second member 11C,wherein the lower end has an opening enabling communication between asupply path 113C of the second member 11C and the inside of the barrel181C. Then, the supply path 113C leads to the processing chamber AC.

Moreover, the hopper 183C has a heating means such as a heater formaintaining the molten metal at a uniform temperature. It is alsopossible to provide a stirring means for stirring the molten metal MC.

When supplying the molten metal MC, the molten metal MC is poured intothe barrel 181C by the hopper 183C, and at the same time, the screw 182Cis rotationally driven by the motor m1C. Thus, the molten metal MC isextruded from the barrel 181C and supplied to the processing chamber ACthrough the supply path 113C, as shown in FIG. 40.

Here, the molten metal supply unit 18C may also be provided with theabove pressurizing means for applying the injection pressure to theprocessing chamber until the molten metal MC filled into the minutespace 21C is hardened by cooling.

When using such a pressure, including the above-described gas pressureand pressing pressure, not only static pressure but also dynamicpressure can be actively utilized at an early stage of the hardeningstep to perform dynamic pushing by the dynamic pressure. Thus, thecreation of cavities or voids can be avoided more certainly and thefilled molten metal MC can be led to the bottom of the minute space 21Cmore reliably.

Furthermore, the pressurizing by the pressurizing means at the hardeningstep may be performed either independently of or continuously with thepressurizing at the molten metal supplying step. If performedcontinuously, the two pressurizing processes can be integrated into asingle pressurizing process. This can be typically seen in the casewhere the gas pressure is applied with the pressure control unit 13C andthe case where the injection pressure is applied with the molten metalsupply unit 18C. However, regardless of the integration into a singlepressurizing process, it is desirable to adjust the applied pressure.

In addition to such pressurizing, it is also possible to apply at leastone external force selected from a magnetic force and a centrifugalforce. FIGS. 41 and 42 show an embodiment in which the apparatus isprovided with an external force generating means for a centrifugalforce. Here, the portions that have been already described above areomitted from the drawings, except the first member 10C and the secondmember 11C.

The external force generating means includes a vertically standingrotary shaft 191C connected to and rotationally driven by a motor m2C,an arm shaft 192C horizontally attached to the upper end of the rotaryshaft 191C, and wires 193C for suspending the first and second twomembers 10C, 11C from each of the two ends of the arm shaft 192C.

At the hardening step, the rotary shaft 191C and the arm shaft 192C arerotated in a RC direction by rotation of the motor m2C. At this time,the first and second two members 10C, 11C are subjected to a centrifugalforce fC and pulled outwardly from the center of the rotation, as shownin FIG. 42. Thus, the molten metal MC within the minute space 21C isalso subjected to the centrifugal force fC. With the pressure thusapplied by the centrifugal force fC, the molten metal MC can be filledmore reliably into the minute space 21C down to the bottom thereof.

When applying such an external force, preferably, not only staticpressure but also dynamic pressure is actively utilized at an earlystage of the hardening step to perform dynamic pushing by the dynamicpressure. With this method, the creation of unfilled areas at the bottomcan be avoided more reliably by making the molten metal MC certainlyreach the bottom of the minute space 21C.

In the present embodiment, the centrifugal force is adopted as anexternal force, but if a magnetic force is adopted, for example, amagnet may be embedded in the first member 10C to draw the molten metalMC into the minute space 21C using its magnetic force.

The present invention has been described in detail above with referenceto preferred embodiments. However, obviously those skilled in the artcould easily devise various modifications of the invention based on thetechnical concepts underlying the invention and teachings disclosedherein.

1. An electronic device comprising a plurality of stacked substrates,wherein each of said substrates includes a semiconductor substrate, acolumnar conductor, and a ring-shaped insulator, said columnar conductorextends along a thickness direction of said semiconductor substrate,said ring-shaped insulator includes an inorganic insulating layer mainlycomposed of a glass, and said inorganic insulating layer fills aring-shaped groove that is provided in said semiconductor substrate tosurround said columnar conductor.
 2. The electronic device of claim 1,wherein said ring-shaped insulator has insulating layers on inner wallsurfaces of said ring-shaped groove, and said inorganic insulating layerfills said ring-shaped groove that is formed between said insulatinglayers.
 3. The electronic device of claim 2, wherein said insulatinglayer is an oxide layer or a nitride layer.
 4. The electronic device ofclaim 3, wherein said insulating layer is formed by oxidizing ornitriding said semiconductor substrate at the inner surfaces of saidring-shaped groove.
 5. The electronic device of claim 3, wherein saidsemiconductor substrate is a silicon substrate, and said insulatinglayer is a silicon oxide layer or a silicon nitride layer.
 6. Theelectronic device of claim 1, wherein said inorganic insulating layercontains a ceramic component.
 7. The electronic device of claim 1,wherein said semiconductor substrate has a semiconductor device.
 8. Theelectronic device of claim 7, wherein said electronic device is athree-dimensional system-in-package (3D-SiP).
 9. The electronic deviceof claim 8, wherein said electronic device is one of a system LSI, amemory LSI, an image sensor, and a MEMS.
 10. The electronic device ofclaim 1, wherein between adjacent ones of said plurality of substrates,connection conductors are joined to each other through a junction film,and said junction film contains a first metal or alloy component and asecond metal or alloy component having a higher melting point than saidfirst metal or alloy component, whereby a melting temperature is madehigher than the melting point of said first metal or alloy component.11. The electronic device of claim 10, wherein each of said plurality ofsubstrates includes a columnar conductor and a connection conductor, andbetween adjacent ones of said plurality of substrates, the columnarconductor of one substrate is joined to said connection conductor of theother substrate through said junction film.
 12. The electronic device ofclaim 10, wherein said junction film is joined such that said secondmetal or alloy is used as a core and said first metal or alloy componentis applied around said second metal or alloy.
 13. The electronic deviceof claim 10, wherein said first metal or alloy component contains atleast one selected from the group consisting of Sn, In, Bi, Ga and Sb.14. The electronic device of claim 10, wherein said second metal oralloy component contains at least one selected from the group consistingof Cr, Ag, Cu, Au, Pt, Pd, Ni, a Ni—P alloy and a Ni—B alloy.
 15. Theelectronic device of claim 10, wherein said columnar conductor containsat least one selected from the group consisting of Ga, Sb, Ag, Cu and Geand at least one selected from the group consisting of Sn, In and Bi.16. The electronic device of claim 10, wherein a noble metal film isdisposed between said junction film and said connection conductor. 17.The electronic device of claim 16, wherein said noble metal filmcontains at least one selected from the group consisting of Ag, Au, Pdand Pt.
 18. A method for manufacturing an electronic device of claim 10,comprising the steps of: between connection conductors of adjacentsubstrates, applying a junction material containing said first metal oralloy component and said second metal or alloy component having a highermelting point than said first metal or alloy component; and then meltingsaid junction material by a heat treatment.
 19. The electronic device ofclaim 1, wherein said columnar conductor is a metal or alloymelt-solidified product, has an equiaxed crystal area at least in anarea opposed to said substrate, and contains bismuth (Bi) and gallium(Ga) as an inoculant within said melt-solidified product.
 20. Thesubstrate of claim 19, wherein said conductor contains indium (In). 21.The electronic device of claim 1, wherein each of said substratesincludes a first conductor and a junction film, said first conductor isopposed to a bottom face of said columnar conductor, said columnarconductor contains a Sn alloy and fills a through-hole of said substratewith the bottom face opposed to said first conductor at a bottom of saidthrough-hole, said junction film is a metal which is other than noblemetals and has a higher melting point than said Sn alloy, disposedbetween said bottom face of said columnar conductor and said firstconductor inside the bottom of said through-hole, and diffused into saidcolumnar conductor to produce an alloy area, thereby joining said firstconductor to said columnar conductor.
 22. The electronic device of claim21, wherein said junction film is disposed adjacent to a periphery ofsaid columnar conductor.
 23. A method for manufacturing an electronicdevice of claim 21, comprising the steps of on said first conductorformed on said substrate, forming a junction film of a metal materialhaving a higher melting point than a Sn alloy; on said junction film,then supplying a molten Sn alloy for forming the columnar conductor; andletting the metal component of said junction film thermally diffuse intosaid molten Sn alloy at a temperature lower than said melting point,whereby after hardening, said molten Sn alloy has an increased meltingpoint.
 24. A metal filling apparatus for filling a minute space of awafer with a molten metal, comprising a support, a molten metal supplyunit, and a pressurizing means, wherein said support includes aprocessing chamber for processing said wafer, a first member with amounting surface for mounting of said wafer, and a second member with ametal supply path leading to said processing chamber, said processingchamber is defined by combining said first member and said secondmember, said molten metal supply unit is designed to fill said minutespace of said wafer, which is mounted on said mounting surface, withsaid molten metal through said metal supply path, and said pressurizingmeans is designed to apply a pressure to said wafer and said moltenmetal filled into said minute space.
 25. The apparatus of claim 24,wherein said pressurizing means is designed to keep the pressurizedstate until said molten metal is hardened by cooling.
 26. The apparatusof claim 24, wherein said pressurizing is performed using at least oneselected from the group consisting of a gas pressure, a pressingpressure, an injection pressure, a rolling pressure, a centrifugalforce, and a magnetic force.
 27. A conductive composition comprisingfirst metal particles and second metal particles, wherein said firstmetal particles have an average particle size in such a nm range as toexhibit small size effect, enabling melting at a temperature lower thana melting point, and melting of said first metal particles causesmelting of said second metal particles.
 28. The conductive compositionof claim 27, wherein said small size effect is quantum size effect. 29.The conductive composition of claim 27, wherein said average particlesize of said first metal particles is 20 nm or less.
 30. The conductivecomposition of claim 27, wherein said second metal particles have alower melting point than said first metal particles.
 31. The conductivecomposition of claim 27, wherein said first metal particles contain atleast one selected from the group consisting of Ag, Cu, Au, Pt, Ti, Zn,Al, Fe, Si and Ni, and said second metal particles contain at least oneselected from the group consisting of Sn, In and Bi.